Recently, the bulk-edge correspondence has been shown to be violated for the first time in the shallow-water model [1]}, [2]}, that describes oceanic layers on Earth. Once regularized by an odd-viscous term, such a model has a well-defined bulk index: the Chern number. However, the edge picture is anomalous: there exists a family of self-adjoint boundary conditions such that the number of edge modes changes with the choice of boundary condition. The origin of this anomaly is rooted in the unbounded nature of the operator's spectrum and was analyzed via scattering theory and a relative version of Levinson's theorem, originally developed in [3]}.
